Generally, deposition on a long strip of tape is performed through a reel-to-reel method. In this method, two reels are used: one reel is a supply reel for supplying a strip of tape and the other reel is a retreat reel for winding a strip of tape on which specific substance is deposited therearound. Further, according to the reel-to-reel method, since deposition of specific substance and supply and retreat of tape can be continuously performed in a single vacuum chamber, it is possible to produce a long strip of tape having the surface on which specific substance is deposited.
Although the above-described method has an advantage in that it is possible to produce a long strip of tape because deposition area depends on distance between the supply reel and the retreat reel, it also has a disadvantage in that it takes a long period to deposit the specific substance on tape.
There is an improved deposition method (batch-type method) which is capable of shortening deposition period. According to this method, a vacuum chamber has a drum therein, which has a guide groove helically formed on the outer surface thereof, and a long strip of tape is wound along the guide groove. Further, a deposition source is disposed at a side of the drum and the drum is rotated so that specific substance from the deposition source is deposited on the entire surface of the tape by a single time of deposition process. Accordingly, the deposition on a long strip of tape is conducted in a batching method.
However, the batch-type method has a disadvantage in that a length of tape which can be wound along the guide groove is limited according to size of the drum. That is, in order to obtain a long strip of tape having the surface on which specific substance is deposited, a large size of drum is needed. In this case, since the drum occupies a large space in a laboratory, manufacturing cost of the deposition apparatus is increased due to the increased size of a vacuum chamber and a pump, and cost and time for operating the large-sized drum is also increased.
Accordingly, in order to solve the above-described problems of the batch-type method, developed is a combined deposition method combining the reel-to-reel method and the batch-type method. That is, a supply reel which supplies a strip of tape to be deposited and a retreat reel for winding a strip of deposited tape are installed at both sides of a shaft of a drum. A tape unwound from the supply reel is moved toward the drum, moved along the guide groove on the surface of the drum and then wound around the retreat reel right after the surface of the tape is deposited with predetermined substance. In this case, since the tape having sufficient length is wound around the supply reel, limitation of the tape length according to the size of drum is obviated. Further, according to this method, it is possible to deposit a substance on a large surface area, and the advantage of the batch-type method also can be enjoyed.
However, this method also has a disadvantage in that edges of tape are likely damaged because there is tension of tape due to frictional force between the tape and the drum because the long strip of tape is in contact with the guide groove of the drum when the tape is moved. Under circumstances, it also can happen that the tape is never moved when the total frictional force is too high.
This problem can be a cause of degradation of superconductive property of a high temperature superconductive film deposited on tape at high temperature in the case where the specific substance formed on the tape is a high temperature superconductive film. The high temperature superconductive film is generally made of ceramic. Accordingly, if tension is exerted to the tape, the superconductive film made of ceramic and formed on the tape can have fine cracks. This causes decrease of threshold current, resulting in degradation of superconductive property.